This is really a strange question. A conical horn should do just fine. It will sound a bit coloured anyway and a conical horn carries far away. Maybe you can modify one of the cones that children get when they enter school.

yeah horn's color the sound, there is a dropoff. maybe i can design it that way that it doesn't does that in my vocal range. but i guess that is gonna be one big horn if it may not cutt of just up to 80-90hz.